The prior art includes the evacuation of shavings, swarf and other loose solid materials by means of slatted conveyors, conveyor belts, intermittent scraper blades, alternate-operating pushers and screw-feeders with semi-cylindrical or cylindrical housing adhering to the screw. The system generally operates in a trench with infeed and discharge only by gravity, with transportation mainly in a horizontal or slightly inclined direction or, sometimes, in a vertical direction.
DE-A-2 806 334 teaches a screw conveyor for conveyance of shavings of a machine tool, comprising a screw eccentrically enclosed in a conveyor tube and driven by a motor imparting to the screw an intermittent rotation. At the inside of the conveyor tube longitudinal rails are provided in order to break up the shavings, thus preventing the entanglement of the shavings.
GB-A-2 056 399 teaches a system for conveying metal shavings comprising a trough inside which a feed screw is arranged. A lip extends parallel to, and the whole length of, the feed screw to prevent shavings from being wound around the feed screw and also to cut up any long shavings. The system includes a disintegrator followed by a second feed screw.
Furthermore, it is known from JP-Abstracts vol.9, No. 142 (M-388) (1865) a chip discharging apparatus wherein the chips are dropped into a cylindrical guide pipe and transported along the pipe by a revolving coil spring. The screw feeders according to DE-A-2 806 334 and GB-A-2 056 399 consists of screws offering a high ratio (e.g. greater than 3) between the external diameter and that of the shaft; moreover their threads are often of low thickness, of the order of a few millimeters for external diameters of for example 200 mm: thus their use is inevitably limited to the conveyance of shavings falling within the category of granular or powder materials well known to be suitable for conveyance by usual screw-feeders. If long metal shavings are to be conveyed, said screw feeders require means to break up the shavings which involve an additional motive power.
The discharging apparatus according to JP-Abstracts, vol.9, no. 142, makes use of a revolving coil spring as a conveyor. This kind of conveyor can not compact the shavings which maintain a high specific volume and require separate compacting devices.
All kinds of shavings, or materials in general, require an evacuation method appropriate to the different characteristics of the material.
During handling of shavings or materials in general by various conventional means, many problems may often arise: for example, long metal shavings easily form tangled masses when transported by means of a slatted conveyor, and the slats may be damaged by the entangled shavings and blockages and cause hold-ups in operation and wasted time.
Furthermore, it must be noted that transportation by means of slatted conveyors, in a horizontal or slightly inclined direction is the only option available for long metal shavings, since scraper blades and conventional screw feeders are unsuitable because said shavings tend to become entangled in the blades, and to wind round the screw without moving forward, thus blocking the feed of the material which follows. As to the use of a pusher for conveying long shavings, the efficiency level is too low since the system operates on a very high apparent specific volume in discontinuous mode.
Short shavings can be conveyed by scraper blades and pushers, even if with low efficiency and high time wastage, while in the case of granular or powdery shavings, as already mentioned, the conventional screw feeder can be used as a horizontal or, less frequently, vertical evacuation system.
In all cases, the material is collected at the end of the transportation phase in removable containers into which the materials fall by gravity: this is of extremely low efficiency for those materials, such as long shavings, having high apparent specific volume.
There is also a system for the transportation of metal shavings by means of a shaftless screw thread operating inside a basically semi-cylindrical housing: however, said system tends to have the problem of blocking caused by tangles and does not provide compacting of the material. In order to compact the material, the system must incorporate compactors comprising an alternating pusher whose sole function is pressing and not directly connected to the machine, but generally disposed at a distance therefrom; said pusher discharging the block or pad of shavings sideways in intermittent fashion.
The prior art stands in need of considerable improvements with regard to the possibility of identifying a method for evacuation of bulk materials which eliminates the problems described above and which enables the provision of a new evacuation machine capable of operating with a wide range of bulk materials, including the most problematical, and which is capable of being used individually for reception, evacuation, conveying and initial compacting, but is also suitable for use in association with other equipment and/or with a number of conveyor elements, including screw feeder, also providing compacting, in order to constitute a plant for conveying materials in a wide range of directions (including vertical climbs or routing at any incline), for chopping, compacting (including in blocks), collection in containers and pressing in the case of metal shavings or other materials containing liquids, such as machine tool coolants, in order to separate the components from each other.
From the above there derives the need to solve the technical problem of finding a new method of conveying bulk materials which provides the continuous feed of the same under pressure, even in the case of long, thin, ductile, tangled and/or loose metal shavings which are difficult to convey, reducing the apparent specific volume of said materials significantly to allow their continual, compacted transfer from the production or initial free collection zone, along routes leading in any direction, to the storage, transformation, destruction or discharge point. This method is required to provide a new type of evacuation machine capable of injecting the material, even of heterogeneous nature, after an initial compacting, into compacting containers, or of conveying the same along conveyor elements to a plant for its final collection, in a suitably compacted state, in containers into which the material enters by gravity fall, or in blocks. Where necessary, it must also be possible for the material to be transferred from the conveyor outlet into a container which may be located higher than said conveyor outlet.
The invention solves the above technical problem by adopting a method which involves the infeed of the bulk material onto a continuous screw conveyor exhibiting an advantageously low ratio between the external diameter of the threads and the diameter of the shaft, one or more longitudinal paths open towards the screw thread being provided outside a cylinder tangent to the screw thread, said paths being provided in order to prevent the bulk material from adopting a path around the circumference of the screw without moving forward and, at the same time, to allow the material to be compacted and to be fed onwards in a direction parallel to the screw axis.